1. Field of the Invention
This invention relates generally to fluid pressure brake systems and particularly to automatic application valves as used in such systems.
2. Description Of The Prior Art
In air brake systems, especially in tractor-trailer combinations, a problem exists in that air pressure applied at the tractor portion must actuate the trailer brakes which are physically located substantial distances from the tractor. As a result, time delays exist between the air brake application at the tractor and air brake actuation at the trailer. To reduce such time delays, valves and systems were devised whereby an air supply was provided in proximity to the trailer brakes and a relay valve was provided adjacent that air supply. In addition, since an electrical impulse can move between two points faster than an impulse moved by air pressure, electrical means were provided to actuate the relay valve for releasing air pressure to actuate the trailer brakes inasmuch as electrical signals could actuate the trailer brakes almost simultaneously with application of the brakes at the tractor thus avoiding the previously known time delays. Such systems are of the type shown and described in U.S. Pat. Nos. 3,747,992 and 3,796,468. Unfortunately, the systems of the prior art are not compatible with skid control systems unless a novel relay valve is provided in the system.